National League for Nursing (NLN PAX) Practice Exam

The presence of guard cells in plants primarily regulates water loss. Guard cells are specialized cells located on the surfaces of plant leaves and stems, surrounding the stomata, which are tiny openings that allow gas exchange. By controlling the opening and closing of these stomata, guard cells play a crucial role in minimizing water loss through transpiration.

When environmental conditions are favorable, such as during the day when photosynthesis occurs, guard cells swell with water, causing the stomata to open. This allows carbon dioxide to enter the leaf for photosynthesis while also releasing oxygen. However, when conditions are dry or during hot weather, guard cells lose water and shrink, leading to the closing of the stomata. This action helps to conserve water within the plant, preventing excessive water loss.

While photosynthesis efficiency does relate to the function of guard cells because the opening of stomata facilitates carbon dioxide uptake, the primary role of guard cells is fundamentally tied to the regulation of water loss to maintain plant health and water balance. Guard cells do not directly influence growth height or root spread, as these processes are governed by different mechanisms and factors in plant biology.